In the typical printer technology, a laser is used as a light source in a printer head to scan and transfer the printing information to a rotating drum. The best advantage of using a laser in a printer head is that the scattering phenomenon is almost eliminated. However, the optical structure is quite complex and difficult to reduce in size for using a laser in this way. Therefore, the current trend is toward using light emitting diodes to replace lasers as the light sources in printer heads, which can simplify the optical structure.
FIG. 1 is a schematic diagram of a conventional printer. The light emitting diode arrays 102 in the printer head 100 are the light source. When printing, the light from the light emitting diode arrays 102 illuminate the rotating drum 106 through a focusing prism 104. Static electricity is produced in the illuminated regions of the rotating drum 106. The carbon held in the toner cartridge 108 is attracted by this static electricity generated in the rotating drum 106. The attracted carbon is printed onto a paper 110 via the rotating drum 106. Next, the paper 110 is heated to fix this carbon in place.
A light emitting diode is related to a point of the image being developed on the paper. In other words, the resolution of a printer is related to the number of light emitting diodes per unit area. For example, a printer with 600 dpi resolution requires about 5000 light emitting diodes in the printer head for printing an A4 size paper. Therefore, the printer head 100 is composed of twenty-six light emitting diode arrays 102, wherein each LED array 102 is composed of 192 light emitting diodes to form printing points.
A further requirement is to reduce the volume of each light emitting diode so as to increase the resolution of the printer. More light emitting diodes may be constructed per unit area in the printer head when the volume of each light emitting diode is reduced. According to the typical packaging method as illustrated in FIG. 2, a highly precise packaging apparatus is required to arrange the light emitting diode arrays 102 and the driver integrated circuits 112 so that they are exactly parallel to each other in a printed circuit board 114. Then, a wire bonding process is performed to form about 5000 wires 116 between the light emitting diode arrays 102 and the driver integrated circuits 112 if the resolution of the printer is 600 dpi. The driver integrated circuits 112 drive the light emitting diode arrays 102 through these wires 116.
A highly exact and dense wire bonding process in the foregoing method increases the difficulty of the packaging process. This reduces the product yield and indirectly raises the manufacturing cost. Moreover, reducing the volume of the light emitting diodes, although increasing the resolution of the printer, further increases the packaging difficulty.
Furthermore, according to the typical packaging method, the wire bonding process is performed after all the driver integrated circuits and the light emitting diode arrays are arranged in the printed circuit board. Therefore, the electrical connection detection is performed after the wire bonding process. Consequently, if a defective light emitting diode array or driver integrated circuit is found, the reworking process includes dismantling the failed product from the printed circuit board and replacing it with a new product. This reworking process is difficult and tedious.
Therefore, a new package structure and method thereof is required to resolve the foregoing problems.